Treatment of citrus trees infested with nematodes



United States Patent TREATMENT OF CITRUS TREES INFESTED WITH NEMATODESGrace A. MacKay, Upland, Calif.

N0 Drawing. Application July 6, 1954, Serial No. 441,660

13 Claims. (CI. 47-58) This invention relates to treatment of citrustrees infested with nematodes; and it comprises a method of treatingcitrus trees infested with nematodes and having such symptoms asshriveling and loss in yield of fruit, defoliation, lack of new growth,drying and dying of branches followed by eventual death, usually withoutany other apparent manifestation of disease symptoms above the ground.My treatment consists in treating the ground around and theroot systemof a tree infested with nematodes with a dilute aqueous solution ofiodine, for example by constructing a wall around the tree to form abasin or well capable of holding at least from about to gallons ofwater, then adding a dilute aqueous solution of iodine to the basin inamount sufiicient thoroughly to wet the root system of the tree and theground around it at least out to the drip of the tree and preferably toa distance of about 2 feet or more beyond the drip of the tree, thisiodine treatment being advantageously followed and/or preceded bythoroughly soaking the ground around the tree with water; all as morefully hereinafter set .forth and as claimed. 7 V

This application is a continuation-in-part of my copending priorapplications, Serial No. 325,452, filed December 11, 1952, now PatentNo. 2,734,314, and Serial No. 346,805, filed-April 3, 1953 and nowabandoned. In the earlier of these two prior applications I described atreatment for scaly bark, more correctly .psorosis, in

which'a dilute aqueous iodine solution is applied directly to theaffected parts of the tree, such as the trunk and branches. A treatmentfor brown rot gummosis and mal di gomma is also described. In the lattertreatment a relatively more dilute iodine solution is applied to theground around the afilicted tree and also, of course, inherently to theroot system of the tree, by saturating the ground with the dilute iodinesolution. These two treatments are, of course, applied quitedifferently.

In Serial No. 346,805 I originally and erroneously reported that thetreatment for brown rot gummosis and maldi gomma described in the firstapplication is also effective in curing or at least remitting thesymptoms of quick decline. The present application is filed principallyto report my discovery that the trees to which I had successfullyapplied my iodine treatment, as disclosed in Serial No. 346,805, andwhich I thought were afliicted with quick decline, because of a faultydiagnosis by an expert, were actually afilicted by an infestation ofcitrus nematodes rather than quick decline and that surprisingly mytreatment is eflective in controlling and/or eradicating this pest. Thename slow decline has been frequently used to designate an ailment whichhas later been established as being due to the depredations ofnematodes.

As reported in my copending application, Serial No. 346,805, my firstexperience with what an expert diagnosed. as quick decline came when Inoticed late one Januarythat one tree in the most southern row of mygrove appeared to be dead while 8 others were badly affected, the leavesbeing wilted and turning brown while 2,742,736 Patented Apr. 24,- 1956the fruit had failed to size and had wrinkled. I called in an expert andhis report read, Quick decline. Nothing whatever can be done about it.It cant be cured. He recommended prompt removal of all 9 trees andreplacement with stock alleged to be resistant to this disease. InsteadI started digging around the dead tree to determine if possible justWhat had killed it. I removed the soil to a depth of about 40 inches andexposed the tap root. Each inch on the way down revealed a dryer anddryer condition. The soil around the tap root was bone dry. It wasevident that the tree had died basically from lack of moisture and food.

Instead of removing the other afiected trees as recommended I firstattempted to revive them by water alone, feeding their roots with waterpassed through auger holes and soaking the ground around them by makingbasins or wells about the trees and filling with water. After aninterval of about a week the trees showed some improvement but threeweeks later they were again on the sick list. I then decided to try myremedy already found successful for treating brown rot gummosis.

In this treatment I employed 7% tincture of iodine solution diluted 1 to16. In treating each of the .8 trees I first made up a dilute batch ofiodine solution by adding the diluted iodine preparation to 5 gallons ofwater. The amounts added to the 5 gallon batches were varied to produceiodine concentrations varying from batch to batch from 0.01 to 0.1% byweight. Each tree was treated with one of these batches by pouring onehalf, i. e. 2 /2 gallons into a 6 foot diameter well about the tree,while the remaining 2 /2 gallons, after dilution with water 1 to l, wassprayed on the surrounding ground out to the drip of the tree. No othertreatment was used except that after an interval of 6 hours the soil wassprayed with water for one hour. Every one of the 8 trees thus treatedhas since recuperated fully and is now bearing normally, therehabilitation being so swift that it seemed like a miracle.

The most dilute iodine solution introduced into the well in one of thesetests had an iodine concentration of about 0.01% while that sprayed onthe ground was half of this. The most concentrated solution containedabout 0.1% iodine by weight.

During my experiments with the described root system iodine treatment Ibecame suspicious that what I was treating was not a disease, strictlyspeaking, but rather an infestation of citrus nematodes. The variouspublications which I read on this subject described symptoms, namelyloss in yield, yellowing and falling of foliage, lack of new growth,drying out and dying of branches and eventual death of the trees, whichwere identical to those encountered in my grove and which had beendiagnosed by experts as being due to quick decline. I learned thatnematodes propagate very rapidly and soon after birth bury their headsin the fine feeder roots of a citrus tree and thereafter suck from theroots the life sustaining sap. This would account for the dehydrationand starvation of the trees which I had treated.

I could find no satisfactory way of testing for the presence ofnematodes myself; the services of an expert in this field were obviouslyrequired. So I sent to such an expert one sample of soil and feederroots taken from a tree which was badly afflicted but which I had notyet had the opportunity to treat with iodine and a second similar sampletaken in the same way from an afilicted tree which I.had treated asdescribed below with iodine about a month previously. This expertreported, as I had suspected, that the first sample contained largenumbers of live nematodes, while the second sample also 7 containednematodes, but that these nematodes were dead.

These tests proved to me that'I had been successfully combatting with myiodine treatment an infestation of citrus nematodes. Apparentlynematodes are killed by free iodine, possibly due to the fumigatingaction of the latter. Iodine vapors are heavy and after my treatmentpenetrate the soil for a substantial depth. To my knowledge this is thefirst successful treatment for nematodes which can be applied to thesoil and the root system of a citrus tree without killing or injuringthe tree. Other treatment for killing nematodes in the soil, which havebeen used commercially, are known to kill or injure plant life. Howeverit has been reported in the literature that, when certain seeds andbulbs and the roots of strawberry plants, infested with nematodes, havebeen dipped in solutions of iodine, the nematodes have been killed.

In the particular treatment used on the citrus tree, the root sample ofwhich was reported as containing dead nematodes, I had built a basinaround a large tree, hav ing a diameter of about 21 feet and extendingout to about 2 feet beyond the branches, i. e. beyond the drip of thetree. The basin was constructed by piling up a ring of dirt around thetree to a height of about 6 to 8 inches. This basin was first filledwith water which was allowed to soak in. The basin was then again filledwith water. To this was added about gallons of water with which a cupfull (about 8 ounces) of 7% tincture of iodine had been mixed. Thisdilute iodine solution was made up in a 5 gallon pressure sprayer andwas sprayed uniformly over the surface of the water in the basin. Afterthe resulting dilute solution of iodine in the basin had soaked in thebasin was again filled with water. That completed the treatment. Withinabout to days after this treatment a few new leaves appeared along theformerly bare branches and within a few weeks new leaves appeared on thewhole tree. No further symptoms of dehydration or starvation havesubsequently appeared.

A more general description of my method of treating a citrus treeinfested with nematodes can be outlined as follows:

1. If the tree has any dead limbs or branches, remove them and seal allWounds. Then clean out beneath the tree and level soil by raking.

2. Test for plow sole to see if water can penetrate the soil. If agarden fork cannot penetrate a lower layer, use a soil auger, to make atleast 4 holes per tree at least 2 feet deep. These should be spaced atequal distances about the tree and several feet from the trunk.

3. Form a basin by throwing up a soil retainer made not by ditching butby adding enough soil to form a raised dirt wall around the tree 8inches high at the drip of the tree or 2 feet outside the drip of treesthat are widely spaced. If the acreage being treated has a slope of morethan 10 inches from the tree drip at the top of the basin to the treedrip at the lower side then better results are obtained using two halfcircles, one half being higher than the other, as this will more evenlydistribute the iodine solution around the tree.

4. Fill the basin slowly with water and let it sink in while preparinganother tree.

5. Refill basin with water then mix in uniformly from about /2 to 2 cupsof 7% tincture of iodine in alcohol. The tincture of iodine shouldpreferably be first mixed with about 5 gallons of water and this mixturedistributed and mixed uniformly with the water in the basin. It can besprayed uniformly on the surface of the water or distributed by pouringsmall portions about every three feet around the basin and stirring witha rake, for example. If a 5 gallon pressure sprayer is available thiscan be filled with water, the tincture of iodine added and mixed in,followed by spraying of the dilute iodine over the surface of the waterin the basin.

6. After the iodine solution has soaked in fill the basin to capacityand let stand. No further treatment should be required for 9 months or ayear. No harm will be done if an excess of iodine is used. It makeseverything to which it is applied grow vigorously.

7. An easier but somewhat less satisfactory method of applying theiodine to citrus trees can be used by those who do not have waterpressure available. This makes use of a water tank like that used by allpest control companies. The tank is filled with dilute iodine solutionmade by mixing 8 ounces of 7% tincture of iodine per 5 gallons of water.The ground around the trees is then sprayed with this dilute iodinesolution immediately after the trees are irrigated. For each 5 gallonsof the dilute iodine solution in the tank from about /2 to 4 trees canbe treated.

8. It is important that treated trees, especially if cut back and alwaysin the heat of summer, be irrigated twice a month. Young and small treesshould receive amounts of solution in proportion to their size.

9. The iodine solution should not be applied to dry soil and be left todry since the iodine would soon sublime and be lost. But if carried intothe soil with water it will last a long time. In one case the roots andsoil about a tree were examined six weeks after an iodine treatment,during which period 6 inches of rain had fallen. But iodine was stillpresent in the soil.

The basic feature of my method is to apply iodine to the soil about acitrus tree out at least to the drip of the tree at the rate of fromabout 1.5 to 15 grams per tree or from 0.05 to 0.5 gram per square footof soil treated about the tree for basins ranging in size from about 20to 6 feet in diameter, and to wash this iodine into the soil with water.The manner in which the iodine is applied to the soil and the manner inwhich it is washed in are of secondary importance so long as the iodineis not wasted by sublimation. Of course the water present in the diluteiodine solution employed in my process tends to wash the iodine into thesoil and when highly dilute iodine solutions are used this water may besufficient alone without the subsequent application of water. This istrue particularly when the soil is wet, as by irrigation, before theiodine is applied. The chemicals which are present in the iodinesolution aside from the iodine are also largely of secondary importanceprovided that they are non-toxic and non-reactive with the iodine. Thus,since iodine is soluble in water to the extent of about 0.04% it ispossible to employ a saturated solution of pure iodine in the treatment.However it is much more convenient to prepare the dilute iodine solutionused in the treatment by suitably diluting the ordinary tincture ofiodine.

Tincture of iodine is sold in a mild preparation containing per ml. fromabout 1.8 to 2.2 g. iodine and from about 2.1 to 2.6 g. NaI dissolved inalcohol of from about 43 to 50% by volume. Strong tincture of iodinecontains from 16 to 17 g. iodine and 2 to 4 g. KI dissolved in 100 ml.alcohol of from about 60 to 65% by volume. These preparations can beused in my process if diluted to the proper degree. It is also possible,of course, to supply to the trade highly concentrated solutions ofiodine in various iodine solvents containing dissolving agents, such asaqueous alkali metal iodide solutions or water-miscible organicsolvents, such as low molecular alcohols, acetone, ethylene glycol,glycerine etc. with instructions that the preparations be diluted to theproper degree.

It is also possible to supply the iodine in the form of capsules ortablets to be dissolved in a given quantity of water. A tabletcontaining about 1.5 to 15 g. iodine can be used for treating one tree,for example, after being dissolved in 5 to 10 gallons of water. Analkali metal iodide should be included in these tablets since thisspeeds the dissolution of the iodine and also helps to prevent theiodine from subliming. The amount used per tablet can vary widely, butapproximately as much iodide should be included as iodine. An additionalamount up to about 5 g. per tablet is advantageous. If desired othercompatible agents capable of retarding sublimation of the iodine can beadded to the tablets. It is also possible decline. This treeis justnorth of my home and positioned between twofiowergardens.v wGne day-r1noticed that .this :tree had shed its bloom 'early before -fruithad*fdrrriedrsatisfactorily. Soon after-its *leaves started turningy'ellow, some limbs soon appeared nearly bare of leaves. Then onemorning I found one limb dead and another with many "deadfruitwoodbranches and few oranges l'ft onthe-tree had-turned -asicklyyellow green. The diagnosis aof'zan -expert wasquick decline. Myfirst conclusion was too much water. This was a "natural fcorficlus'ionsince'iithe gardens on either side had receivtedfan'i'ple water.*Bufitfted for-moisture and was surprised tofiiid 'thatthe "soihiibo'utthetrunk was-so devoid of moisture and so compact that penetration wasmost difficult. The two denuded branches died and were removed. I thendecided to apply my iodine treatment. This was accomplished by forming a6 foot diameter well about the tree. In making upv the iodine treatingsolution I first diluted tincture of iodine (7%) with water 1 to 16,then added a pint of this to 5 gallons of water. One half of this batchwas poured into the well while the remainder was diluted 1 to l withwater and sprayed on the surrounding ground out as far as the branchesextended. After a delay of 6 hours the ground was thoroughly watered.The tree responded so wonderfully to this treatment that it now has twonew branches to replace the lost ones and an abundant covering ofleaves. It is now again a healthy tree.

In one of my treatments I have started with removing all leaves andother debris from a circular area around the tree trunk then forming awell capable of holding about 20 gallons of water. The soil isthoroughly cultivated. About 10 gallons of water are then poured intothe well. Then when the soil has absorbed the water the well is floodedwith about 20 gallons of dilute iodine solution, this being formed byadding about one gill of tincture of iodine to about 20 gallons ofwater, resulting in an iodine concentration of about 0.01% by weight.The iodine solution is poured slowly around and also on the tree trunktaking care that it directly reaches all affected areas of trunk androots. This treatment may be repeated in about days but one applicationis usually adequate. As yet I have found no afiiicted tree requiring athird application of iodine. The trees so treated have been completelyrejuvenated.

In still another treatment which I have used successfully a diluteiodine solution is prepared by adding a gill of tincture of iodine to 12quarts of water. The soil about the tree is first saturated with about10 gallons of water, the dilute iodine solution is then applied andallowed to soak in and finally the iodine is washed in by an additional10 quarts of water to carry it down to the bottom of the infected rootarea.

While I have described what I consider to be the most advantageousembodiments of my process it is obvious, of course, that variousmodifications can be made without departing from the purview of thisinvention. Thus it is possible to include in my iodine preparationswetting agents, such as cationic soaps, non-ionic or anionicsurface-active agents, such as sodium naphthenic sulfonate and cetylpyridinium iodide, which are non-toxic and nonreactive with iodine. Alarge number of suitable wetting agents are now commercially available,being sold as synthetic detergents. Any of these can be used which arecompatible (non-reactive) with iodine and non-toxic. These can be addedin concentrations ranging from about 0.005 to 0.1% and assist in makingthe iodine solution penetrate the soil. The iodine in my preparationscan be either in dissolved or emulsified form. In making theconcentrated preparations which are distributed to the trade it isimportant to employ materials which are nonmaterial is likely to betoxic to citrus trees. "It is possible,

"ofcourse, to employ 'several'iodine treatments. When the more -'diluteiodine solutions are used and in the case of "badly-afilicted treesfitwotreatments can be administered "six months apart-at the time of growingperiods which "are spring and 'fall. If several treatments are used,these should"be= spaced-apart at-least from aboutZ to 4 weeks. -But,'asstated previously, one treatment is usually'adequate. The actualmethodof applying my dilute iodine solutions tofthe so'ilsis"notimportant.Thus soil a'ugers jcanfbeietnployed' to drill a'se'ries of holesabout'the "afilictedhree and these holes 'flooded with the-iodinesolution. lt is also possible to employ a hose equipped wit'ha metalpipewhichcan bein'seftdintd thesoilto a depth of a foot or more andmaking-use of an iodinecontaining capsule :ina by pass 1 chamber in thenozzle,

the tree and about its roots to a depth of at least from about 6 inchesto 3 or more feet with a dilute iodine solution which has aconcentration ranging from about j 0.005% up to concentrations tendingto damage the tree.

I have not accurately determined this upper toxic limit but believe itis between about 0.5 and 1% by weight. I have used concentrations up toabout 0.2% iodine. There is no point in using such high concentrations,however, since much more dilute solutions will accomplish satisfactoryresults. Further modifications of my process which fall within the scopeof the following claims will be immediately evident to those skilled inthis art.

What I claim is:

1. In the treatment of citrus trees infested with nematodes andaccompanied by such symptoms as shriveling and loss in yield of fruit,defoliation, lack of new growth, drying and dying of branches followedby eventual death, the process which comprises thoroughly saturating thesoil around such an afilicted tree with a highly dilute aqueous solutionof iodine having a concentration ranging from about 0.005% up to butbelow concentrations tending to damage the tree and washing the iodineinto the soil with water.

.2. The process of claim 1 wherein the iodine solution has aconcentration ranging from about 0.005 to 0.5% by weight.

3. The process of claim 1 wherein the iodine is applied to the soilabout the tree out at least to the drip of the tree at the rate of fromabout 1.5 to 15 grams iodine per tree.

4. The process of claim 1 wherein the iodine solution is added to abasin surrounding the tree at the rate of from about 0.05 to 0.5 gram ofiodine per square foot of soil in the basin.

5. The process of claim 1 wherein the dilute iodine solution is made byadding tincture of iodine to the required amount of water.

6. The process of claim 1 wherein the soil is saturated by forming abasin around the tree having a diameter of at least about 6 feet andadding from about 2 /2 to 20 gallons of the iodine solution to thebasin.

7. The process of claim 6 wherein the soil outside the basin and out tothe drip of the tree is also saturated with the iodine solution.

8. The process of claim 1 wherein the dilute iodine solution is added toa basin built around the tree and extending outward-s to a distance ofabout 2 feet beyond the drip of the tree.

9. The process of claim 1 wherein the iodine solution contains anon-toxic compatible wetting agent to assist penetration of the soilwith the iodine solution in concentrations ranging from about 0.005 to0.1% by weight.

10. The process of claim 1 wherein the iodine solution is sprayed on theground surrounding such a tree just after irrigation of the tree.

11. In the treatment of citrus trees infested with nematodes andaccompanied by such symptoms as shriveling and loss in yield of fruit,defoliation, lack of new growth, drying and dying of branches followedby eventual death, the process which comprises forming a basin aboutsuch an afliicted tree having a diameter ranging from about 6 to 20feet, distributing uniformly in said basin a highly dilute solution ofiodine having a concentration ranging from about 0.005 to 0.5% byweight, letting the iodine solution soak into the ground and thenwashing the iodine into the soil by filling the basin with water andletting it soak in.

12. The process of claim 11 wherein the iodine solution contains fromabout 1.5 to 15 grams of iodine.

13. The process of claim 11 wherein the iodine solution iii containsfrom about 0.05 to 0.5 gram of iodine per square foot of soil in thebasin.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Iodine and Plant Life, pub. 1944 by Chilean IodineEducational Bureau, London, England; pp. 80-83.

Biological Abstracts, vol. 25, p. 1970, Entry 21,675, pub. 195 l.

1. IN THE TREATMENT OF CITRUS TREES INFESTED WITH NEMATODES ANDACCOMPANIED BY SUCH SYMPTOMS AS SHRIVELING AND LOSS IN YIELD OF FRUIT,DEFOLIATION, LACK OF NEW GROWTH, DRYING AND DYING OF BRANCHES FOLLOWEDBY EVENTUAL DEATH, THE PROCESS WHICH COMPRISES THOROUGHLY SATURATING THESOIL AROUND SUCH AN AFFLICTED TREE WITH A HIGHLY DILUTE AQUEOUS SOLUTIONOF IODINE HAVING A CONCENTRATION RANGING FROM ABOUT 0.005% UP TO BUTBELOW CONCENTRATIONS TENDING TO DAMAGE THE TREE AND WASHING THE IODINEINTO THE SOIL WITH WATER.